Duplexer having two non-reciprocal phase shifting means



Aug. 25, 1970 w. w. slEKANowlcz ET AL 3,525,952

RECIPROCAL PHASE SHIFTING MEANS DUPLEXER HAVING TWO NON- Filed Sept. 30,1968 2 Sheets-Sheet l SN QN m ww m m N%\ gdm@ wmw. \|||\...m m www. m-..Ill Il. l l l -IVA lllllmwd l JST A www0 QN @QN .Xmw m Aug- 25. 1970w. w. slr-:KANowlcz ET AL 3,525,952

DUPLEXER HAVING TWO NON-RECIPROCAL PHASE SHIFTING MEANS Filed Sept. 30,1968 2 Sheets-Sheet 2.

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United States Patent 3,525,952 DUPLEXER HAVING TWO NON-RECIPROCAL PHASESHIFTING MEANS Wieslaw W. Siekanowicz, Trenton, Donald J. Blattner,

Princeton, and Thomas E. Walsh, Kearny, NJ., assignors to RCACorporation, a corporation of Delaware Filed Sept. 30, 1968, Ser. No.763,774 Int. Cl. H01p 1/32, 5/14 U.S. Cl. S33-1.1 10 Claims ABSTRACT FTHE DISCLOSURE A duplexer includes a center dual waveguide section. Aferrite toroid is placed along the length of one waveguide section, anda Xed 180 differential phase shift is provided along the length of thesecond waveguide section. A first and a second short-slot hybrid couplerrespectively terminates each end of the center duel wavef guide section.A latching wire is passed through the ferrite toroid in the firstsection and coupled to a current driver. Upon the application of a pulsefrom the driver in one direction, an additional 180 relative phase Shiftis provided for signals traveling in a lirst direction along the lengthof the rst waveguide section than for signals traveling in the oppositeor second direction through the waveguide section. Upon the applicationof a pulse from the driver in the opposite direction, an additional 180relative phase shift is provided for signals traveling in the second oropposite direction through the rst waveguide section than for signalstraveling in the first direction through the section.

BACKGROUND OF THE INVENTION This invention relates to duplexers and moreparticularly to duplexing systems employing ferrite elements.

Duplexing systems utilizing ferrite elements for coupling a transmitterand a receiver to a common antenna and providing isolation between thereceiver and the transmitter are known in the art. One common methodutilizes a ferrite junction circulator. A single circulator does not,however, provide adequate isolation for the relatively high power duringthe transmission from a transmitter such as used in airborne radarsystems. Additional isolation is therefore needed and may be provided bya series of serially connected latching circulators which, upon commandfrom a current driver, change their direction of circulation. Inaddition to the number of circulators required to meet the requiredisolation, the circulators are sensitive to temperature changes and theisolation is dependent upon the level of RF power. Also, if the currentdriver fails while the circulator is in the receiving condition, thetransmitter power will not be isolated from the receiver causingbreakdown of the receiver.

It is therefore an object of the present invention to provide animproved duplexer which is relatively insensitive to temperature changesand operates at a relatively high level of RF power, providing betterreceiver protection by absorbing the reflected power during transmissionby the transmitter and by providing a fail-safe operation in the eventof current driver failure.

This and other objects of the present invention are accomplished by theuse of two independent phase Shifters having two `conditions ofadjustment. The phase Shifters are coupled between two hybrid sectionswherein power' splitting and a 90 relative phase shift between thewaveguide sections occurs. In one condition of adjustment, a 180relative phase difference occurs between signals traveling in a givendirection through one of the waveguide sections and signals traveling inthe one direction Ffice through the other waveguide section. In a secondcondition, both waveguide sections provide an equal amount of phaseshift for signals traveling in the opposite direction through thewaveguide sections.

A more detailed description follows in conjunction with the followingdrawings wherein:

FIG. 1 shows a perspective exploded view of one embodiment of a duplexerin accordance with the invention,

FIG. 2 s a cross sectional view of the center Lsection of waveguides 17and 19,

FIGS. 3 and 4 respectively are diagrams used to illustrate the operationof the duplexer in the signal transmitting and signal receivingconditions respectively, and

FIG. 5 is a diagram illustrating the operation of the duplexer when theduplexer is in the receive condition and the transmitter `signals areapplied.

Referring to IFIG. 1, the duplexer comprises a center waveguide section10 between two similarly constructed waveguide hybrid sections 13 and15. The center section is made up of two adjoining rectangularwaveguides 17 and 19 which may have a common wall 18 extending theentire length of center section 10. A rst ferrite toroid 20 hasadjoining matching `dielectric pieces 20a and 20b on either end. 'Ihetoroid 20 and the dielectric pieces 20a and 20b are centered alongwaveguide 17. The ferrite toroid 20 and dielectric pieces 20a, 20b havean aperture 23 along the length thereof. The toroid 20 and dielectricpieces 20a and 20'b are mounted between the broad walls of the waveguide17 A latching wire 25 is looped through the toroid 20 and dielectricpieces 20a and 20b by passing the wire through the aperture 23. A driver218` is coupled to the latching wire 25 and provides a fixeddifferential phase shift of through the waveguide section 17 upon theapplication of DC. current pulses in one direction along the wire 25.Because of the closed magnetic flux path in the ferrite toroid 20, asshown by the arrows in FIG. 2, the toroid operates at a remanentmagnetization after termination of the current pulse. The phase shi-ftthrough the ferrite is determined by the properties and dimensions ofthe ferrite, and by the orientation of the magnetization with respect tothe direction of RF propagation. The length of the ferrite toroidsection 20, 20a, 20b is adjusted such that, for the direction of D C.magnetization shown in FIG. 2, the phase shift through the waveguidesection 17 will be 180 greater for a wave traveling from the transmitterto the antenna than for a wave traveling in the opposite direction.

A second toroid 21 centered along waveguide 19 also has adjacentmatching dielectric sections 21a and 21b on either end of the toroid.The ferrite toroid 21 and dielectric pieces 21a, 2lb have an aperture 24along the length thereof. The toroid 21 and dielectric pieces 21a, 2lbare mounted between the broad walls of the waveguide 19. A latching wire`26 is looped through the toroid 21 and dielectric pieces 21a, 21b bypassing the wire through the aperture 24. A driver 29 is coupled to thelatching wire 26 and provides switching of the toroid 21 by applyingunidirection pulses of DC. current in opposite directions along they'wire 26. The driver 29 may in practice be the same driver as driver 28wherein a diode is placed in the latching Iwire 25 and suitably poled toprevent reversing of the phase shift through toroid 20. Because of theclosed magnetic flux path in the ferrite toroid 21 as shown in FIG. 2,the toroid operates at a remanent magnetization after termination of thecurrent pulse. The phase shift through the ferrite is determined by theproperties and dimensions of the ferrite and the orientation of themagnetization with respect to the direction of RF propagation. Theferrite toroid 21 provides along the length of the ferrite a 180diiferential phase shift between signals traveling in oppositedirections through waveguide 19. By applying D.C`. current pulses of onedirection (positive going from driver 29) signals passing on onedirection, i.e., from transmitter to antenna undergo an additional 180phase shift whereas signals passing in the opposite direction from theantenna to the receiver or transmitter undergo additional phase shift.By applying upon command D.C. pulses of opposite direction (negativegoing, for example) from driver 29, signals passing in the oppositedirection from the antenna to the receiver or transmitter undergo anadditional 180 phase shift through that section.

`On either side of the center waveguide sections 17 and 19 are locatedend hybrid waveguide sections 13 and 15. These are identical directionalcouplers which are conventional broad-band, short-slot hybrids 'wherebypower splitting and 90 relative phase shifting occurs bet-Ween waveguidesections 31 and 32 of hybrid 13 with passage of signals through slot 33in the common wall of hybrid waveguide section 13. Likewise, 90 relativephase shifting and power splitting between waveguide sections 35 and 36of hybrid 15 is provided -with passage of signals through slot section37 in the common wall of waveguide section 15. While the hybrid sectionsare symmetrically bidirectional, the ends thereof adjacent the centralwaveguide may be considered the inputs of the hybrids and their otherends may be the outputs thereof.

In the described arrangement the transmitter, not shown, is located atterminal 41 which is the outboard end of waveguide section 35 and thereceiver, not shown, is coupled to terminal 42 which is the outboardportion of ywaveguide section 36. The inboard section of Waveguide 35joins with waveguide section 17 and the inboard section of waveguide 36joins with waveguide section 19. The outboard portion of waveguidesection 31 is coupled to a dummy load (not shown) at terminal 43 and theoutboard portion of waveguide section 32 is coupled to antenna terminal44.

The operation of the dupleXer of the invention, as shown in FIG. 1, willbe described in connection with the diagrams of FIGS. 2 and 3 whichindicate by the arrowed straight and curved lines the distribution ofthe signal energy as it appears in the duplexer in the signaltransmitting or receiving condition respectively of the associatedsystem coupled thereto.

Turning now to the transmitting condition, the relative phase shiftthrough the various regions of the duplcxer are indicated in FIG. 3. TheRF signal from the transmitter at terminal 41 undergoes a power splitand 90 relative phase shift between the split signals in passing throughthe short-slot hybrid coupler in section 15. In passing through centersection 10, an additional 180 phase advance is provided in passingthrough the ferrite loaded waveguide sections 17 and 19. Signal energypassing through waveguide section 17 and coupled through the short-slotof hybrid 13 undergoes an additional power split and 90 relative phaseshift when passing through this hybrid section.

Since the signal energy that would emerge from terminal 43 at the dummyload suifers destructive interference, namely one is 0.5 360 and theother being 0.5 l80, all the power (0.5 270-|-0'.5 270 or amplitude-:1)emerges from port `44 or the antenna port. Any reflected signals at theantenna terminal 44- undergo zero additional relative phase shiftthrough waveguides 17 and 19 and consequently these reflected signalswill suffer destructive interference at the receiver (-0.5 0 and 0.5180). The reflected signal will therefore be reected back to thetransmitter terminal 41 (0.5 90 and 0.5 90) and will not be reflected tothe receiver, thereby providing isolation of the receiver from thetransmitted signals.

This isolation of the receiver from transmitter power is insensitive totemperature because the two ferrite clements, toroids 20 and 21, performidentical functions in the transmit condition. Thus, if a temperaturechange caused the phase shift through 17 to change, the phase shiftthrough 19 would undergo the same change. Also, any power reflected fromantenna terminal 44 would still have destructive interference at thereceiver; similarly, all power from the transmitter emerges at theantenna, thereby providing full isolation at the receiver.

Turning to the receive condition, the relative phase shift through thevarious regions of the duplexer are as indicated in FIG. 4. To switch tothe receive condition, a D.C. pulse of opposite direction (negativegoing) is provided from driver 29 which reverses the differential phaseshift through waveguide section 19 so that signals traveling from theantenna to the receiver have an additional phase shift 4of 180 andsignals from the receiver to the antenna have 0 additional phase shift.The signal from the antenna is power split and relative phase shift isprovided by hybrid section 13. The signals when passing throughwaveguide section 17 from the antenna undergo no additional relativephase shift. The .signal passing through waveguide section 19 undergoes180 additional relative phase shift. The signal energy coupled throughthe short-slot hybrid section 15 undergoes additional power split and 90relative phase shift. Signals passing through waveguide section 19 have180 additional relative phase shift. The signal energy adds up (0.5 180and 0.5 180) at the receiver terminal 42. Since the signal energy attransmitter terminal 41 suffers destructive interference, i.e. .5 270and 5 90, all the power (or amplitude :1) emerges at the receiverterminal 42.

A third important advantage of this described arrangement has to doparticularly with the condition wherein, if the driver fails in thereceive condition, the receiver is still protected during transmission.

As illustrated in FIG. 5 the described duplexer is adjusted to receiveand yet the transmitter is operating. Then a power split of thetransmitter signal and a 90 relative phase shift therebetween isprovided by shortslot hybrid waveguide section 15. The passing of thesignals through waveguide section 17 provides 180 additional relativephase shift and the passing of the transmitter signals through waveguidesection 19 provides no additional relative phase shift. Power split and90 relative phase shift of the transmitter signals is provided at hybrid13. At the antenna port 44 these signals (0.5 270 and .5 90) sufferdestructive interference and the signal energy adds up (.5 180 and .5180) at the dummy load terminal 43. All the power (amplitude :1) isapplied to the dummy load which absorbs most of the power appliedthereto. Any reiiections from the dummy load add up at the transmitterterminal and suffer destructive interference at the receiver, it beingremembered that for signals passing in towards nthe receiver throughwaveguide 17, the phase shift is zero, and for signals passing throughthe waveguide 19 towards the receiver, the phase shift is Therefore, thereceiver is protected even though the system has failed in the receiveposition.

A device as described above was constructed and tested and provided aminimum of 40 db of isolation and operated over a frequency range of5400 iSO megahertz and over a temperature range of -40 C. to +75 C. Thisdevice had the following characteristics:

The length of the dual center waveguide section 10 is 4l/2 inches. Thelength of the hybrids are each 31A inches. The length of the ferritesections 20 and 21 is 3.6 inches. The length of each dielectric matchingsection 20a, 2Gb, 21a and 21h is 320 mills.

The ferrite material has a dielectric constant of 15; and the dielectricmatching sections 20a, 2Gb, 21a and 2lb have a dielectric constant of 6.

While what has been described herein is one embodiment of the presentinvention using short-slot hybrids and differential phase shifters, itis understood that the present embodiment is only by way of example.Numerous other changes such as magic tees in place of short-slot hybridsmay be used, and also other phase Shifters such as adjustable reciprocalphase Shifters may be used rather than differential phase Shifters toprovide the 180 additional relative phase shift in one phase Shifterthan the other phase shifter for signals traveling in a rst direction inboth phase shifters and to provide no additional relative phase shift inone phase Shifter than the other phase shifter for signals traveling inthe second direction opposite the first direction through both phaseShifters.

What is claimed is:

1. In combination,

a central dual waveguide having rst and Second Sections,

first means coupled to each end of said dual waveguide and providing ateach end power splitting with 90 relative phase shift of signals appliedthereto,

Second adjustable means having two conditions of adjustment,

in one condition of adjustment, said second means providing anadditional 180 relative phase shift of signals propagating in onedirection through one waveguide section than for signals propagating insaid one direction in the other waveguide section of said dual waveguideand,

in said second condition of adjustment said second means providingvirtually no difference in relative phase shift of signals propagatingin the opposite direction through said one waveguide section than forsignals propagating in said opposite direction in the other waveguidesection of said dual waveguide.

2. The combination as claimed in claim 1 wherein said second meansincludes at least one ferrite toroid in at least one of said waveguidesections and further includes a pulse driver and a latching wire coupledto the pulse driver and passing through the center of the toroid.

3. The combination as claimed in claim 2 wherein Said rst means includestwo short-slot hybrids, one coupled to each end of said dual waveguide.

4. The combination as claimed in claim 1 wherein said second meansincludes a differential phase Shifter in said one waveguide section anda second differential phase shifter in said other waveguide section.

5. The combination as claimed in claim 4 wherein said rst means includestwo short-Slot hybrids, one coupled to each end of said centralwaveguide.

6. The combination as claimed in claim 4 wherein said phase Shiftersinclude ferrite toroids.

7. The combination as claimed in claim 5 wherein Said Second meansincludes a ferrite toroid in said one Waveguide section.

8. The combination as claimed in claim 7 wherein said Second meansincludes a pulse driver and a latching wire coupled to the pulse driverand passing through said second ferrite toroid in said one waveguidesection.

9. A duplexer comprising,

a pair of hybrid means each having two input portions and two outputportions, a wave applied to either one of said input portions appearingin equal amplitudes and out of phase at said output portions, while thewave applied to either one of said output portions appears in equalamplitude and 90 out of phase at said input portions,

a pair of reversible phase shifters through which waves may travel inboth directions, said phase Shifters each providing a phase shift in onedirection of wave travel therethrough that is equal to a constant valueplus and providing a phase shift in the other direction of wave traveltherethrough that is equal to Said constant value, and

means to reverse one of said pair of phase Shifters whereby a wavetraveling therethrough in said one direction is shifted in phase by saidconstant value and a wave traveling therethrough in the oppositedirection is shifted in phase by Said constant value plus 180,

each of said Shifters being arranged to receive waves from and totransmit waves to a respective output portion of one of said hybridmeans and to transmit waves to and receive waves from a respectiveoutput portion of the other of said hybrid means.

10. The combination as claimed in claim 9 wherein said phase Shiftersinclude toroids.

References Cited UNITED STATES PATENTS 2/1961 Walsh 333--10 X 5/1962Chait et al. 333-1.1

U.S. Cl. X.R. S33-40, 24.1

